What is the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km per hour?

Last updated at June 8, 2019 by Teachoo

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NCERT Question 17 Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h? Mass of car = m = 1500 kg Velocity of the car = v = 60 km/hr = 60 × 5/18 m/s = 10 × 5/3 m/s = 50/3 m/s Conversion from km/h to m/s 1 km = 1000 m 1 hour = 60 minutes = 3600 s ∴ (1 𝑘𝑚)/ℎ = (1000 𝑚)/(3600 𝑠) ∴ 1 km/h = 5/18 m/s Work done = Kinetic energy of the car I nitial Kinetic energy = 1/2 mv2 = 1/2 × (1500) × (50/3)^2 = 1/2 × 1500 × (50/3×50/3) = 1/2 × 1500 × 2500/9 = (500 × 2500)/(3 × 2) = (250 × 2500)/3 = 208333.3 J Since the car eventually stops Final Kinetic Energy = 0 Now, Work done = Change in Kinetic energy = 208333.3 – 0 = 208333.3 J Work done is 208333.3 J

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Ans. The kinetic energy of the car is zero as it stops. So, the work done that is required to stop the car will be equal to its kinetic energy.

Given,

Mass of car, m = 1500 kg

Velocity of car, v = 60 km/h

= 60 x 1000/60 x 60

= 50/3

We know that,

Kinetic energy = mv2

= 1/2 × 1500 ×(50/3)2

= 1500 x 2500/2 x 9

= 208333.3 J